Semi-visible higgs decay as a probe for new invisible particles

TL;DR

This paper explores the potential of the High-Luminosity LHC to detect new invisible particles via semi-visible Higgs decays, using an effective theory framework to analyze decay kinematics and distinguish operator structures.

Contribution

It introduces a novel analysis of semi-visible Higgs decays within a dark-SMEFT framework, providing strategies to identify different operator structures of invisible particles.

Findings

HL-LHC can probe invisible particles below 50 GeV mass.

Kinematic strategies can distinguish operator structures.

Results compare favorably with Z-width constraints and unitarity bounds.

Abstract

We discuss the HL-LHC sensitivity to probe new invisible particles including scalars and fermions using semi-visible Higgs decays. The kinematics of these decays allow new particle masses below $m\lesssim 50$ GeV. We carry out our analysis within the framework of a dark-SMEFT effective theory with operators up to dimension six and a discrete $\mathbb{Z}_2$ symmetry under which the new particles are odd and the SM particles are even. We compare our results to those obtained from considering the invisible $Z$-width, as well as simple perturbative unitarity arguments. Finally, we outline kinematic strategies at the LHC to distinguish different operator structures of the postulated invisible particles.